1. Field of the Invention
The present invention relates to an intake control device particularly for a vehicle engine.
2. Related Art
The rpm (revolution per minute: output power) of an engine used in a motorcycle or automobile is controlled by opening/closing a throttle valve provided in an intake air path introducing an intake air into a cylinder so as to increase or decrease an amount of the intake air flowing into the cylinder.
An idle speed control (ISC) has been known as a countermeasure against changeover time or variations that would occur due to a throttle bore clogged with carbon, for example. To execute the ISC, a bypass air path should be provided to communicate with upstream and downstream sides of the throttle valve in an intake air path to control an air flow rate in the bypass air path.
As an example of an intake control device for carrying out the ISC, there is a device provided with a main throttle valve and a sub-throttle valve in an intake air path, and in addition, a bypass communicating with upstream and downstream sides of the main throttle valve. The bypass is also provided with an ISC valve, and the ISC valve and the sub-throttle valve are independently controlled with an ECU, for example (see Japanese Unexamined Patent Application Publication Nos. 06-108904 and 06-146940).
Further, there is another device including a main path constituting an intake air path and an, auxiliary path constituting a bypass parallel to the main path, in which the main path is provided with a main valve and the auxiliary path is provided with an auxiliary valve. Both the valves are coaxially and rotatably integrated, and an air control valve is separately provided in the auxiliary path, for example (see Japanese Unexamined Patent Application Publication No. 05-180038).
Further, there is still another intake control device including a main throttle valve and a sub-throttle valve in an intake air path and operating the sub-throttle valve to perform FID control, for example (see Japanese Unexamined Patent Application Publication No. 2002-129987).
However, as for the devices described in Japanese Unexamined Patent Application Publication Nos. 06-108904 and 06-146940, driving actuators should be arranged for each valve in order to independently control the ISC valve and the sub-throttle valve with the ECU. As a result, the device structure is made complicated or a device cost increases.
Further, in the case of separately providing the air control valve in the auxiliary path as described in Japanese Unexamined Patent Application Publication No. 05-180038, the ISC is executed by driving the air control valve. In this case, even if the air control valve is fully opened, the auxiliary valve and the main valve are both fully closed, so that this technique is unsuitable for the ISC.
Moreover, the intake control device described in Japanese Unexamined Patent Application Publication No. 2002-129987 requires a complicated link mechanism for transmitting a rotative force of the sub-throttle valve to the main throttle valve, leading to the complicated device structure and an increase in device cost.
In addition, the above device has the following drawback. It is difficult to apply the device to the ISC that requires high-precision and high-accuracy control compared with the FID control in consideration of machining errors or dimensional tolerances of transmission units and joints in a complicated link mechanism.